<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    
  </style>
</head>
<body>
  <div class="the_div">
    <p>我是p标签</p>
    <h3>我是h3</h3>
    <h3>我是h3</h3>
    <h3>我是h3</h3>
    <a id="theA" href="#">我是一个a标签</a>
    <ul>
        <li>北京</li>
        <li>天津</li>
        <li>南京</li>
    </ul>
    <ol class="my_li">
        <li>大张</li>
        <li>大王</li>
        <li>大狗</li>
    </ol>
    <ul class="my_li">
        <li>小明</li>
        <li>小红</li>
        <li>小蓝</li>
    </ul>
</div>

<script>
  // 练习1
  const a = document.querySelector('#theA');
  console.log(a);
  // 练习2
   const h31 = document.querySelector('h3:nth-child(2)');
   const h32 = document.querySelector('h3:nth-child(3)');
   const h33 = document.querySelector('h3:nth-child(4)');
   console.log(h31);
   console.log(h32);
   console.log(h33);
  //  练习3
  const lis = document.querySelectorAll('li');
  console.log(lis);
  // 练习4
  const lis1=document.querySelectorAll('ul.my_li li');
  console.log(lis1);
  // 练习5
   const lired=document.querySelector('ul.my_li li:nth-child(2)');
   lired.innerHTML=`小六`
   lired.style.color = 'red'
  //  练习6
  const litj= document.querySelector('ul li:nth-child(2)');
  litj.className= 'green'
  litj.style.backgroundColor= '#087'
</script>
</body>
</html>